Submarine U-570: The WW2 submarine captured by an aircraft

In August 1941 the British Admiralty suspected their communications were being intercepted by the Germans.

To test their theory, they transmitted a dummy message. It gave details of an upcoming movement of allied merchant ships off the south Icelandic coast.

Would the Germans respond?

They did.

The German code breakers of B-Dienst picked up the message.  And on August 23rd a wolf pack of sixteen U-boats was sent to Iceland to attack and sink the group.

One of them was U-570 – a newly-built type VIIC Class diesel submarine with 44 crew on board.

The captain was Hans-Joachim Rahmlow and it was his first time in charge of a U-boat. He had completed only six months of training on submarines before taking command of U-570.

His two senior officers were also first-timers and the crew were naval rookies. This was the first war mission for everyone on board.


Iceland Map

Location of the U-570 when it surfaced.


By the time U-570 approached Icelandic waters, they had been battling through very rough seas for several days.  Many of the crew were suffering severe seasickness. Desperate to give his crew some relief, the inexperienced captain decided to ignore his orders, and surface.

But they were only 80 miles from Iceland and the submarine was immediately spotted by a disbelieving crew of RAF No. 269 Maritime squadron.

Sergeant Les Mitchell was part of an anti-submarine patrol based at the newly built RAF Kaldadarnes airbase, on the southwest shore of Iceland.


Lockheed Hudson aircraft

Lockheed Hudson anti-submarine aircraft


After spotting the submarine near the surface, in the clear Arctic sea, he quickly circled his Lockheed Hudson back over it and launched depth charges. But frustratingly the delivery rack mechanism jammed. Determined not to lose it, he radioed the U-boat’s position and stayed in the area until more units from his squadron arrived.


U570 Pumping Fuel

The U-570 pumping out fuel to lighten the submarine


Down below, Captain Rahmlow was unaware he’d been seen.

He was so intent on getting fresher air on board for his sick seamen, he breached the surface without raising his periscope to check the area was clear.

At that same moment, No. 269’s Squadron Leader, James Thompson, arrived on scene. Despite his surprise at the submarine surfacing, he reacted fast, flew towards the vessel and launched depth charges from an altitude of 100 feet.

On the bridge of the U-570, Rahmlow heard the approaching plane’s engines and ordered an emergency dive.

But he was too late.

Thompson’s four 250-pound depth charges plunged into the sea around the submarine.

The U-570 rushed forward to try and avoid a direct hit. But the explosives detonated just yards away from the submarine. And shock waves slammed into it, almost rolling it over.

Power systems inside the submarine failed.  It started to take on water through the damaged hull and as this seeped into the engineering section, leaking battery acid mixed with sea water creating gas. The rookie crew panicked.


U570 Crew

Some of the U-570 crew crammed into the conning tower


Lacking experience, and thinking his vessel was filling with toxic gas, the captain ordered his crew to put on lifejackets and prepare to abandon the submarine. Crewmen crammed into the conning tower, some waving a white sheet at the circling aircraft.

Meanwhile on the bridge Rahmlow gave orders to destroy their Enigma machine and code books. He also radioed for help, but forgot to encode the message.

Enigma code machine

German Enigma code machine


The British intercepted it and ordered all available allied ships to the area at full speed. The U-570 was not going to escape. Captain Rahmlow was also warned that he and his crew would be fired on if they tried to scuttle their vessel or make a run for it.

The Germans surrendered.

U570 Boarding Party

Boarding party approaching the U-570


After many hours overcoming several issues, including deteriorating weather conditions, British crew from the support vessel HMS Kingston Agate eventually boarded U-570.

Astonishingly, while securing the submarine, they discovered Enigma code books and files in the radio room.  In their rush to destroy the equipment, the German crew had overlooked them.

They contained paired messages, along with the coded and decoded versions of each one.  A huge breakthrough for the Bletchley Park code breaking team working on deciphering the Enigma codes.


U-570 Enigma Code books

German Enigma code books


The German seamen were transferred to HMCS Niagara, and the captured submarine was towed to Iceland, escorted by aircraft from RAF No. 269 squadron.

After undergoing repairs to make her seaworthy, the U-570 then sailed under her own power to Barrow in England, where the British Royal Navy and the United States Navy went over every part of the submarine in detail.  It gave them the chance to learn more about the German U-boats.


U-570 in Barrow UK

Captured U-570 arriving in Barrow shipyards, England


For the next couple of months, U-570 went through a major refit and on October 5, 1941, it changed sides – commissioned into the Royal Navy as HMS Graph.

After completing sea trials in Scotland, HMS Graph carried out patrols in the Atlantic, across the Bay of Biscay and later around the fjords of Norway.


U-570 Submarine

HMS Graph on route to be be dismantled, 1943.


In June 1943 she was finally decommissioned.

But while on her way to be dismantled, the submarine ran aground near Saligo Bay in the treacherous waters around Islay, a small island off the west coast of Scotland.

Sadly HMS Graph joined the many wrecks that litter the coast of this island and remained there until she broke up in 1961.

For their part in capturing the U-570, Squadron Leader James Thompson and Flying Officer William Coleman received the Distinguished Flying Cross.




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